This invention generally relates to air conditioning systems that provide a heating function. More particularly, this invention relates to air conditioning systems having multiple indoor units in fluid communication with an outdoor unit for providing heat to a plurality of rooms or sections within a building.
Building air conditioning systems take a variety of forms. Most systems have an outdoor unit with a compressor and a coil assembly. Indoor units may be a single unit having a fan assembly and a coil assembly. Other systems have multiple indoor units, each with their own fan and coil assemblies.
Some air conditioning systems are capable of providing cooling during warm temperatures and heat during cooler outdoor temperatures. When multiple indoor unit systems (xe2x80x9cmultiplex systemsxe2x80x9d) provide a heating function, it is desirable to control the amount of refrigerant charge within the system. Under some circumstances, not all of the indoor units need to operate to adequately heat the various portions of a building and, therefore, part of the overall system is inactive. Under such circumstances, it is possible for the level of refrigerant charge to become undesirably high or undesirably low within the active portion of the system. The system operation may be impaired when there is too much or too little refrigerant within the active part of the system (i.e., that part of the system including the indoor units that are currently heating). When there is too much refrigerant within the active part of the system, excessively high discharge pressures may occur. When there is too little refrigerant in the active part of the system, there is typically a loss of heating capacity and the possibility for increased ice formation on the coil of the outdoor unit.
One attempt at managing refrigerant charge in the active part of such a system is to include shutoff valves upstream of the indoor units. When a particular indoor unit is not required to be active, the shutoff valve closes off refrigerant flow from the outdoor unit to the inactive indoor unit or units. While this approach is useful, it includes the shortcoming of requiring additional charge up time at the indoor units when they are eventually needed for heating. Another drawback of this approach is that the reduced flow through the overall system increases the pressure in the active lines and causes hotter air to be discharged by the active indoor units, which may provide uneven heating within a building space and inefficient system operation.
There is a need for a more efficient refrigerant charge management approach within multiplex air conditioning systems that provide heat to a building space. This invention addresses that need while avoiding the shortcomings and drawbacks of prior approaches.
In general terms, this invention is a method and system for controlling the level of refrigerant charge within an air conditioning system having an outdoor unit and multiple indoor units where the indoor units are individually controllable so that not all of them necessarily are active at the same time.
A system designed according to this invention includes an outdoor unit having a compressor and a coil assembly. A plurality of indoor units are located within a building, each including its own fan and coil assembly. Supply and return lines connect the outdoor unit to the indoor units. A flow control device controls the amount of return fluid flow from the indoor units to the outdoor unit. A controller controls the flow control device to selectively vary the amount of refrigerant flowing downstream from any inactive indoor units so that the overall refrigerant charge level in the active part of the system is controlled within desirable levels.
In one example, each of the return lines from the indoor units includes a modulating expansion valve. A controller controls each of the valves to control an amount of refrigerant fluid returning from the indoor units to the outdoor unit and the active part of the system.
A method of this invention includes determining when the refrigerant charge level in the active part of the system is outside of a desirable range. Refrigerant fluid is allowed to flow into all of the indoor units, even those that are inactive at any given time. The amount of fluid flow returning from the inactive units is controlled to thereby control the amount of refrigerant charge level in the active part of the system.
When the refrigerant charge in the active part of the system is too low, an increased return flow from the inactive units is permitted. When the refrigerant charge level in the active part of the system is too high, refrigerant fluid is effectively stored within the inactive units for at least some period of time.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawings that accompany the detailed description can be briefly described as follows.